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EP1286439B1 - Semiconductor optical device and method of manufacturing the same - Google Patents

Semiconductor optical device and method of manufacturing the same Download PDF

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Publication number
EP1286439B1
EP1286439B1 EP02018467A EP02018467A EP1286439B1 EP 1286439 B1 EP1286439 B1 EP 1286439B1 EP 02018467 A EP02018467 A EP 02018467A EP 02018467 A EP02018467 A EP 02018467A EP 1286439 B1 EP1286439 B1 EP 1286439B1
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Prior art keywords
layer
doped
diffusion
inp
semiconductor
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English (en)
French (fr)
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EP1286439A2 (en
EP1286439A3 (en
Inventor
Matsuyuki NTT Int. Property Center Ogasawara
Susumu Kondo
Ryuzo NTT Int Property Center Iga
Yasuhiro NTT Int. Property Center Kondo
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Nippon Telegraph and Telephone Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
    • H01S5/0265—Intensity modulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/227—Buried mesa structure ; Striped active layer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2054—Methods of obtaining the confinement
    • H01S5/2059—Methods of obtaining the confinement by means of particular conductivity zones, e.g. obtained by particle bombardment or diffusion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
    • H01S5/2222—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special electric properties
    • H01S5/2226—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special electric properties semiconductors with a specific doping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/227—Buried mesa structure ; Striped active layer
    • H01S5/2275—Buried mesa structure ; Striped active layer mesa created by etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
    • H01S5/3072—Diffusion blocking layer, i.e. a special layer blocking diffusion of dopants

Definitions

  • the present invention relates to semiconductor optical devices and a method of manufacturing them and, more particularly, to a semiconductor optical device having two sides of an active region buried in a semi-insulating crystal and a method of manufacturing the device.
  • a semi-insulating burying heterostructure having a semi-insulating layer as a burying layer is used for a semiconductor optical device such as a semiconductor laser diode or semiconductor optical modulator. It is known that when this structure is used for such a device, lower device capacitance and higher speed modulation can be realized than when a p-n buried structure is used. For this reason, a semi-insulating burying heterostructure is indispensable to semiconductor optical modulators and semiconductor optical devices used for a high capacity optical transmission system.
  • a semiconductor crystal doped with iron (Fe) is conventionally used for such a semi-insulating burying heterostructure. If, however, iron (Fe) is used as a dopant, interdiffusion of iron (Fe) as a dopant for a semi-insulating burying layer and zinc (Zn) as a dopant for a p-cladding layer and p-contact layer of the device occurs at the interface between the semi-insulating burying layer and the device. As a consequence, as zinc is diffused into the burying layer, the characteristics of the device deteriorate, resulting in a deterioration in modulation characteristics.
  • interdiffusion is not limited to the case wherein Zn is used as a p-impurity, and other p-impurities such as Be, Cd, and Mg also cause interdiffusion with Fe.
  • reference numeral 31 denotes a semiconductor substrate; 32, a buffer layer; 33, an active layer; 34, a cladding layer; 35, a contact layer, and 36, an Fe diffusion preventing layer.
  • US 5 717 710 A discloses an optical semiconductor device comprising a DFB laser integrated with a light absorption modulator, wherein an iron doped semi-insulating burying layer is disposed between a carrier blocking layer and a upper cladding layer.
  • a semi-insulating burying layer arranged on two sides of a layer forming a mesa stripe including an n-cladding layer, active region, and p-cladding layer is constituted by a diffusion enhancement layer which is adjacent to the mesa-stripe-like multilayer structure and enhances diffusion of a p-impurity, and a diffusion suppression layer which is adjacent to the diffusion enhancement layer and contains a semi-insulating impurity that suppresses diffusion of the p-impurity.
  • a. monolithically integrated light source including a semiconductor laser and an electroabsorption optical modulator as defined in claim 6.
  • a method of manufacturing a semiconductor optical device wherein a semiconductor laser and an optical modulator are monolithically integrated on a semiconductor substrate as defined in claim 8.
  • a semiconductor optical device according to the present invention will be described in detail below by using the embodiments.
  • Fig. 1 shows a case wherein a semiconductor optical device according to the present invention is applied to a semiconductor laser having an MQW (multiple quantum well) active layer.
  • MQW multiple quantum well
  • a 0.2 ⁇ m-thick Se-doped n-InP cladding layer 2 is formed on a (100) oriented n-InP substrate 1.
  • a 40 nm-thick undoped InGaAsP guide layer 3 having a bandgap wavelength of 1.3 ⁇ m
  • a 0.15 ⁇ m - thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 4 having a lasing wavelength of 1.55 ⁇ m
  • a 40 nm-thick undoped InGaAsP guide layer 5 having a bandgap wavelength of 1.3 ⁇ m
  • a 1.5 ⁇ m-thick Zn-doped p-InP cladding layer 6 and a 0.3 ⁇ m-thick Zn-doped InGaAs contact layer 7 are successively stacked on the surface of the Se-doped n-InP
  • alloy semiconductor layers other than the active layer 4 have compositions lattice-matched to the InP substrate 1 unless otherwise specified.
  • This multilayer structure is processed into a mesa stripe MS having a width of about 2 ⁇ m and a height of about 3 ⁇ m.
  • two sides of the mesa stripe MS are burying in buried layers characterized by the present invention, i.e., Fe-doped InP layers 9 serving as diffusion enhancement layers placed adjacent to the mesa stripe and Ru-doped InP layers 10 serving as diffusion suppression layers placed adjacent to the InP layers 9.
  • the Fe-doped InP layer 9 is located between a side wall of the mesa stripe MS and the Ru-doped InP layer 10 and between the surface of the Se-doped n-InP cladding layer 2 and the Ru-doped InP layer 10.
  • the thickness of the Fe-doped InP layer 9 can be changed as needed. In addition, it suffices if the Fe-doped InP layer 9 is doped with Fe in an amount large enough to induce Zn diffusion.
  • the amount of Ru added to the Ru-doped InP layer 10 should be large enough to sufficiently make this layer semi-insulating.
  • the Fe-doped InP layer 9 is formed at least between a side wall of the mesa stripe MS and the Ru-doped InP layer 10.
  • the Fe-doped InP layer 9 is not always required between the surface of the Se-doped n-InP cladding layer 2 and the Ru-doped InP layer 10.
  • An SiO 2 passivation film 11 is formed on the entire surface except for the surface portion immediately above the mesa stripe MS.
  • a p-electrode 12 is formed on the surface of the InGaAs contact layer 7 immediately above the mesa stripe MS.
  • An n-electrode 13 is further formed on the bottom surface of the n-InP substrate 1.
  • the device according to the present invention differs from the conventional device in that the Fe-doped InP layer 9 using as a diffusion enhancement layer is inserted between a side wall of the mesa stripe MS and the Ru-doped InP layer 10.
  • the Fe-doped InP layers 9 have thicknesses (a) 0.1 ⁇ m, (b) 0.4 ⁇ m, and (c) 0.8 ⁇ m, respectively, and their characteristics were compared.
  • the thickness of the Fe-doped InP layer 9 means the thickness of a side of the mesa stripe MS.
  • the resistivities of the buried layers of the three types of devices were about 10 8 ⁇ cm or more. It was found that the formed burying layers had sufficiently high resistances.
  • the small signal modulation characteristics of semiconductor lasers respectively formed into chips were, at a 3 dB bandwidth,
  • the threshold current and optical output efficiency remained constant regardless of the thickness of the Fe-doped InP layer and were about 10 mA and about 35%, respectively. That is, the device characteristics were good except that the device capacitance changed depending on the thickness of the Fe-doped InP layer.
  • the device capacitance decreases as the thickness of the Fe-doped InP layer 9 decreases.
  • the existence of the Fe-doped InP layer 9 using as a diffusion enhancement layer enhances Zn diffusion to decrease defects in the interface between the Zn-doped p-InP cladding layer 6 and the Fe-doped InP layer 9 and reduce leak current, thereby obtaining a semiconductor laser having a low threshold current and high optical output efficiency.
  • a method of manufacturing a semiconductor laser according to this embodiment will be descried with reference to Figs. 2A to 2C.
  • the 0.2 ⁇ m-thick Se-doped n-InP cladding layer 2 having a bandgap wavelength of 1.3 ⁇ m
  • the 0.15 ⁇ m-thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 4 having a lasing wavelength of 1.55 ⁇ m
  • the 40 nm-thick undoped InGaAsP guide layer 5 having a bandgap wavelength of 1.3 ⁇ m
  • alloy semiconductors other than the active layer have compositions lattice-matched to the InP substrate 1 unless otherwise specified.
  • the mesa stripe MS having a width of about 2 ⁇ m and a height of about 3 ⁇ m was formed by RIE (reactive ion etching) using an SiO 2 film 8 as a mask.
  • the Fe-doped InP layer 9 using as a diffusion enhancement layer and the Ru-doped InP layer 10 (thickness: 3 ⁇ m) using as a diffusion suppression layer were grown, by the MOVPE method, on the substrate on which the mesa stripe MS was formed.
  • the Fe-doped InP layer 9 was grown by using known dicyclopentadienyliron (Cp2Fe) as an Fe source. In addition, layer thickness was controlled by the growth time.
  • Cp2Fe dicyclopentadienyliron
  • the Ru-doped InP layer 10 using as a diffusion suppression layer was grown by using bis ( ⁇ 5-2, 4-dimethylpentadienyl) ruthenium (II) was used as an Ru source.
  • the SiO 2 mask 8 was removed, and the SiO 2 passivation film 11 was formed on the entire surface of the resultant structure except for a surface portion immediately above the mesa stripe MS.
  • the p-electrode 12 was then formed, and the n-electrode 13 was formed on the bottom surface of the substrate 1, thereby completing the device shown in Fig. 1.
  • Fe doping concentrations in the Fe-doped InP layers 9 using as diffusion enhancement layers will be described below.
  • the Fe doping concentration means the concentration of Fe, of Fe atoms added into the semiconductor crystal, which were activated as electron compensators.
  • This embodiment is related to an electroabsorption modulator (EA modulator) using InGaAsP/InGaASP multiple quantum wells for a photoabsorption layer.
  • EA modulator electroabsorption modulator
  • the structure of this device is almost the same as that of the first embodiment, and hence will be described with reference to Figs. 1 and 2A to 2C.
  • a 0.2 ⁇ m-thick Se-doped n-InP cladding layer 2 a 40 nm-thick undoped InGaAsP guide layer 3 having a bandgap wavelength of 1.3 ⁇ m, a 0.15 ⁇ m-thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 4 having a lasing wavelength of 1.50 ⁇ m, a 40 nm-thick undoped InGaAsP guide layer 5 having a bandgap wavelength of 1.3 ⁇ m , the 1.5 ⁇ m-thick Zn-doped p-InP cladding layer. 6, and a 0.3 ⁇ m-thick Zn-doped p-InGaAs contact layer 7 were successively stacked on a (100) oriented n-InP substrate 1.
  • alloy semiconductor layers other than the photoabsorption layer have compositions lattice-matched to the InP substrate 1 unless otherwise specified.
  • a mesa stripe MS having a width of about 2 ⁇ m and a height of about 3 ⁇ m was formed by RIE (reactive ion etching) using an SiO 2 film 8 as a mask.
  • an Fe-doped InP layer 9 using as a diffusion enhancement layer and an Ru-doped InP layer 10 (thickness: 3 ⁇ m) using as a diffusion suppression layer were grown, by the MOVPE method, on the substrate on which the mesa stripe MS was formed.
  • the Fe-doped InP layer 9 was grown by using a known material.
  • bis ( ⁇ 5-2, 4-dimethylpentadienyl) ruthenium (II) was used as an Ru source.
  • the SiO 2 mask 8 was removed, and an SiO 2 passivation film 11 was formed on the entire surface of the resultant structure except for a surface portion immediately above the mesa stripe MS.
  • a p-electrode 12 was then formed, and an n-electrode 13 was formed on the substrate side, thereby completing the device shown in Fig. 1.
  • the Fe-doped InP layers 9 have thicknesses (a) 0.1 ⁇ m, (b) 0.4 ⁇ m, and (c) 0.8 ⁇ m, respectively, and their characteristics were compared.
  • the thickness of the Fe-doped InP layer 9 means the thickness of a side of the mesa stripe MS.
  • the resistivity of the overall buried layer of each of the three types of devices was about 10 8 ⁇ cm or more.
  • the small signal modulation characteristics of semiconductor lasers respectively formed into chips were, at a 3 dB bandwidth,
  • the comparison between extinction ratios of these devices reveals that the extinction ratio tends to decrease as the thickness of the Fe-doped InP layer 9 increases. This is because when Zn is diffused into the Fe-doped InP layer 9, Fe is diffused from the Fe-doped InP layer 9 to the p-InP cladding layer 6 due to Zn-Fe interdiffusion. The diffused Fe moves Zn to the interstitial position between lattices by the kick-out mechanism. The Zn moved to the interstitial position is diffused into the photoabsorption layer.
  • This embodiment will exemplify an integrated light source formed by monolithically integrating an electroabsorption optical modulator (EAM) and distributed feedback laser (DFB-LD).
  • EAM electroabsorption optical modulator
  • DFB-LD distributed feedback laser
  • this light source is constituted by the electroabsorption optical modulator (EAM), the distributed feedback laser (DFB-LD), and a groove portion (GP) formed between them.
  • the respective components are formed on a (100) oriented n-InP substrate 1 as a common substrate.
  • a 0.2 ⁇ m-thick Se-doped n-InP cladding layer 2 a 40 nm-thick undoped InGaAsP guide layer 103 having a bandgap wavelength of 1.3 ⁇ m, a 0.15 ⁇ m-thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 104 having a lasing wavelength of 1.50 ⁇ m, a 40 nm-thick undoped InGaAsP guide layer 105 having a bandgap wavelength of 1.3 ⁇ m, the 1.5 ⁇ m-thick Zn-doped p-InP cladding layer 106, and a 0.3 ⁇ m-thick Zn-doped InGaAs contact layer 107 are successively stacked on the (100) oriented n-InP substrate 1.
  • alloy semiconductor layers other than the photoabsorption layer have compositions lattice-matched to the InP substrate 1 unless otherwise specified.
  • the above multilayer structure is formed into a mesa stripe MS having a width of about 2 ⁇ m and a height of about 3 ⁇ m. Two side surfaces of the mesa stripe MS are buried in an Fe-doped InP layer 9 and Ru-doped InP layer 10.
  • An SiO 2 passivation film 11 is formed on the entire surface except for the surface portion immediately above the mesa stripe MS.
  • a p-electrode 112 is formed on the resultant structure.
  • a common n-electrode 13 is further formed on the substrate side.
  • the 0.2 ⁇ m-thick Se-doped n-InP cladding layer 2 a 40 nm-thick undoped InGaAsP guide layer 203 having a bandgap wavelength of 1.3 ⁇ m, a 0.15 ⁇ m-thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 204 having a lasing wavelength of 1.55 ⁇ m, a 40 nm-thick undoped InGaAsP guide layer 205 having a bandgap wavelength of 1.3 ⁇ m and a diffraction grating formed on its upper surface, the 1.5 ⁇ m-thick Zn-doped p-InP cladding layer 6, and a 0.3 ⁇ m-thick Zn-doped InGaAs contact layer 7 are successively stacked on the n-InP substrate 1.
  • alloy semiconductor layers other than the active layer have compositions lattice-matched to the InP substrate 1 unless otherwise specified.
  • the above multilayer structure is formed into a mesa stripe MS having a width of about 2 ⁇ m and a height of about 3 ⁇ m.
  • Two side surfaces of the mesa stripe MS are buried in the Fe-doped InP layer 9 using as a diffusion enhancement layer and the Ru-doped InP layer 10 using as a diffusion suppression layer.
  • the SiO 2 passivation film 11 is formed on the entire surface except for the surface portion immediately above the mesa stripe MS.
  • a p-electrode 212 is formed on the resultant structure.
  • the common n-electrode 13 is further formed on the substrate side.
  • the photoabsorption layer 104 and active layer 204 are optically coupled to each other with a butt-joint configuration. In order to ensure electric insulation, the InGaAsP contact layer 7 is removed.
  • the mesa stripe structure and the burying layers i.e., the Fe-doped InP layer 9 and Ru-doped InP layer 10, are common to the electroabsorption optical modulator portion, distributed feedback semiconductor laser portion, and groove portion.
  • the Fe-doped InP layer 9 and Ru-doped InP layer 10 which are burying layers are formed at once.
  • DFB-LD distributed feedback laser
  • the thickness of the Fe-doped InP layer 9 using as a burying layer must be optimized.
  • the Fe-doped InP layers 9 have thicknesses (a) 0.1 ⁇ m, (b) 0.4 ⁇ m, and (c) 0.8 ⁇ m, respectively, and their characteristics were compared.
  • the thickness of the Fe-doped InP layer means the thickness of a side of the mesa stripe MS.
  • the resistivities of the electroabsorption optical modulator portions and distributed feedback laser portions in the burying layers of the three types of devices were about 10 8 ⁇ cm or more.
  • the threshold currents and optical output efficiencies of the distributed feedback laser portions (DFB-LDs) formed into chips remained constant regardless of the thicknesses of the Fe-doped InP layers 9 and were about 10 mA and about 35%, respectively. These values were obtained when the reverse biases applied to the electroabsorption optical modulator portions (EAMs) were set to zero.
  • the distributed feedback laser portions were lased under constant injection current, and the resultant lasing light intensity was modulated by the electroabsorption optical modulator portions (EAMs). The resultant characteristics were compared with each other.
  • the small signal modulation characteristics of the electroabsorption optical modulators were, at a 3 dB bandwidth,
  • the comparison between extinction ratios of these devices reveals that the extinction ratio tends to decrease as the thickness of the Fe-doped InP layer 9 increases. This is because when Zn is diffused into the Fe-doped InP layer 9, Fe is diffused from the Fe-doped InP layer 9 to the p-InP cladding layer 6 by Zn-Fe interdiffusion. The diffused Fe moves Zn to the interstitial position between lattices by the kick-out mechanism. The Zn moved to the interstitial position is diffused into the photoabsorption layer.
  • the thickness of the Fe-doped InP layer 9 is 0.1 ⁇ m, the threshold current of the distributed feedback laser portion (DFB-LD) is low, and the optical output efficiency is high. In addition, the modulation bandwidth of the electroabsorption optical modulator portion (EAM) is wide.
  • the 0.2 ⁇ m-thick Se-doped n-InP cladding layer 2 the 40 nm-thick undoped InGaAsP guide layer 203 having a bandgap wavelength of 1.3 ⁇ m
  • the 0.15 ⁇ m-thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 204 having a lasing wavelength of 1.55 ⁇ m
  • the 40 nm-thick undoped InGaAsP guide layer 205 having a bandgap wavelength of 1.3 ⁇ m were successively grown on the (100) oriented n-InP substrate 1 by the MOVPE method.
  • the above multilayer structure (the 40 nm-thick undoped InGaAsP guide layer 203 having a bandgap wavelength of 1.3 ⁇ m, the 0.15 ⁇ m-thick strained undoped InGaAsP/InGaAsP MQW (multiple quantum well) active layer 204 having a lasing wavelength of 1.55 ⁇ m, and the 40 nm-thick undoped InGaAsP guide layer 205 having a bandgap wavelength of 1.3 ⁇ m) in the region where an electroabsorption optical modulator (EAM) is to be manufactured is removed by etching.
  • EAM electroabsorption optical modulator
  • the photoabsorption layer 104 of the electroabsorption optical modulator (EAM) is optically coupled to the active layer 204 of the distributed feedback laser (DFB-LD) by butt-joint (BJ) configuration.
  • a diffraction grating DG is formed on the surface of the InGaAsP guide layer 20 in the region where a distributed feedback laser (DFB-LD) is to be manufactured.
  • DFB-LD distributed feedback laser
  • the 1.5 ⁇ m-thick Zn-doped p-InP cladding layer 6 and 0.3 ⁇ m-thick Zn-doped InGaAs contact layer 7 are grown on the entire surface of the resultant structure by the MOVPE method.
  • a mesa stripe having a width of about 2 ⁇ m and a height of about 3 ⁇ m is formed by RIE (reactive ion etching) using an SiO 2 film as a mask 25.
  • Both the electroabsorption optical modulator portion (EAM) and the distributed feedback laser portion (DFB-LD) have the same mesa stripe MS structure.
  • the Fe-doped InP layer 9 using as a diffusion enhancement layer was grown adjacent to the mesa stripe MS, and the Ru-doped InP layer 10 (thickness: 3 ⁇ m) using as a diffusion suppression layer was grown adjacent to the InP layer 9 by the MOVPE method.
  • the Fe-doped InP layer 9 was grown by using a known source material.
  • the SiO 2 mask was removed, and the SiO 2 passivation film 11 was formed on the entire surface of the resultant structure except for a surface portion immediately above the mesa stripe MS.
  • the p-electrode 12 was then formed, and the n-electrode 13 was formed on the lower surface of the substrate 1, thereby completing the device shown in Fig. 3.
  • This embodiment has exemplified the integrated light source in which an active layer of a semiconductor laser and a photoabsorption layer of an optical modulator are coupled by using a butt-joint configuration.
  • the present invention is not limited to this.
  • Identical multiple quantum well (MQW) layers each having an active layer and photoabsorption layer grown together may be used, in which the bandgap energy of the active layers is small, and the bandgap energy of the photoabsorption layers is large.
  • a known selective area growth method may be used to form the active layers and photoabsorption layers. (Japanese Patent Laid-Open No. 1-321677).
  • mask-stripe-like SiO 2 masks are placed on only two sides of a region where an active layer is to be grown, and a multiple quantum well structure is grown by the metalorganic vapor phase epitaxy method. In the region sandwiched between the mask stripes, the well layer becomes thick. The bandgap energy of this region is therefore smaller than that of the remaining regions.
  • an InP crystal is used for the buried layers 9 and 10.
  • a material lattice-matched to InP e.g., InGaA1As, InAlAs, or InGaAsP can also be effectively used.
  • InGaAsP, InGaAlAs, InAlAs MQW layers are used for multiple quantum well layers.
  • the present invention can also be effectively applied to structures such as bulk and multiple quantum well layers in all systems using InP substrates, including an InP-InGaAsP-InGaAs system, InAlAs system, InGaAlAs system, and InGaAs system.
  • Zn is exemplified as a p-impurity
  • the same effects as those described above can also be obtained by using a p-impurity other than Zn, e.g., Be, Cd, or Mg.
  • Se is exemplified as an n-impurity, but the present invention can also obtain the same effects as those described above by using other additives having the same conductivity types as those described above.
  • the semiconductor lasers and optical modulators have been described. Obviously, however, the present invention can also be effectively applied to other semiconductor devices such as semiconductor amplifiers and photodiodes, single devices, and integrated devices such as an optical modulator integrated semiconductor laser and a semiconductor amplifier/light modulator integrated device.
  • the present invention realizes a high-performance buried semiconductor device and is characterized in that a semi-insulating semiconductor crystal used for burying includes two layers, i.e., a layer that enhances impurity diffusion and a layer that suppresses impurity diffusion. This makes it possible to reduce leakage current in the burying interface and suppress an increase in device capacitance.
  • the present invention is characterized in that the semi-insulating semiconductor crystal in which the mesa stripe is buried is constituted by the diffusion enhancement layer containing a semi-insulating impurity that enhances diffusion of a p-impurity and a semi-insulating layer containing a semi-insulating impurity that suppresses diffusion of the p-impurity, the diffusion enhancement layer is inserted between a side wall of the mesa stripe and the semi-insulating layer, and the diffusion enhancement layer is doped with a semi-insulating impurity that enhances interdiffusion with a p-type impurity.
  • the semi-insulating layer outside the diffusion enhancement layer contains a semi-insulating impurity that suppresses diffusion of a p-impurity.
  • the diffusion enhancement layer is doped with a semi-insulating impurity that enhances diffusion of a p-impurity, a p-impurity is diffused from the p-cladding layer, which is in contact with the diffusion enhancement layer, in a burying growth process.
  • the conductivity type of the diffusion enhancement layer changes to the p type. This decreases defects in the interface between the p-cladding layer and the diffusion enhancement layer and reduces leakage current.
  • the semi-insulating layer is doped with a semi-insulating impurity that suppresses diffusion of a p-impurity, the p-impurity is not easily diffused into the semi-insulating layer. This limits diffusion of a p-impurity up to the diffusion enhancement layer.
  • the use of the present invention will produce the noticeable effect of providing a semiconductor device having a structure that can control diffusion of a p-impurity into a semi-insulating burying layer and a method of manufacturing the device.
  • an integrated device is to be formed by using a semiconductor laser (LD) and an EA modulator (electroabsorption modulator)
  • the semiconductor laser and EA modulator often have the same waveguide structure and buried structure.
  • the semiconductor laser portion in order to reduce leakage current, it is necessary to decrease defects in the regrowth interface by enhancing Zn diffusion from the mesa stripe.
  • the EA modulator in order to reduce leakage current, it is necessary to decrease defects in the regrowth interface by enhancing Zn diffusion from the mesa stripe.
  • the EA modulator if the device capacitance increases due to Zn diffusion, high speed modulation cannot be done. It is therefore necessary to properly control the spread of Zn diffusion.
  • the present invention by controlling the impurity doping concentration of the diffusion enhancement layer, a device that meets characteristic requirements for a semiconductor laser and EA modulator can be manufactured.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Geometry (AREA)
  • Semiconductor Lasers (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
EP02018467A 2001-08-21 2002-08-16 Semiconductor optical device and method of manufacturing the same Expired - Lifetime EP1286439B1 (en)

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JP2001249831A JP3654435B2 (ja) 2001-08-21 2001-08-21 半導体光素子及びその製造方法
JP2001249831 2001-08-21

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EP1286439A3 EP1286439A3 (en) 2005-02-02
EP1286439B1 true EP1286439B1 (en) 2006-04-12

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US20030042495A1 (en) 2003-03-06
JP2003060310A (ja) 2003-02-28
EP1286439A2 (en) 2003-02-26
DE60210546T2 (de) 2007-04-05
US6815786B2 (en) 2004-11-09
JP3654435B2 (ja) 2005-06-02
EP1286439A3 (en) 2005-02-02
DE60210546D1 (de) 2006-05-24

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